Holography is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when an imaging system (a camera or an eye) is placed in the reconstructed beam, an image of the object can be seen even when the object is no longer present. The recorded holographic images (or holograms) can change as the position and orientation of the viewing system changes in a similar way as if the object were still present, which can make the image appear three-dimensional. Holograms can include a generally random structure of varying intensity, density or profile. Holograms can be attached to a security document such as driver's licenses, credit cards, bank cards, ID cards, books, DVDs, sports equipment, passports, etc., to authenticate the genuineness of the document. For example, embossed holography has been used in passport documents in many countries.